Firing system for well perforator



June 20, 1961 G. c. THRONER, JR 2,988,993

FIRING SYSTEM FOR WELL PERFORATOR Filed Feb. 15, 1956 2 Sheets-Sheet 1 IN VEN TOR.

6 U Y C. THRO/VER JR.

June 1961 G. c. THRONER, JR 2,988,993

FIRING SYSTEM FOR WELL PERFORATOR Filed Feb. 15, 1956 2 Sheets-Sheet 2 IN VEN TOR. 6U) C. THRO/VER JR.

f M Q? ATTOR/V x 2,988,993 FIRING SYSTEM FOR WELL PERFORATOR Guy C. Throner, Jr., Glendora, 'Califi, assignor to Aerojet- General Corporation, Azusa, Califi, a corporation of Ohio Filed Feb. 13, 1956, Ser. No. 564,896 3 Claims. (Cl. 10221.6)

This invention relates to a novel method and apparahas for effecting substantially simultaneous firing of a group of explosive bodies connected in series'in an electric circuit such as are used in seismic exploration, blasting operations or the detonation of oil well explosives,

such as the shaped charges" used in oil well perforation work.

More particularly, the invention relates to the simultaneous firing of a series of charges contained in a bore hole. The invention is particularly useful for the firing, in an oil well, a series of so-called shaped charges which are in such close proximity to each other that if they were fired in the usual manner, as by a train or cord of high exposives of the type known as Primacord, the delay between successive detonations would result in so-called jet interference. This interference is attributable to a detonation of the second charge by influence from the first charge, often resulting in an asymmetrical detonation, which seriously impairs the efliciency of the jets from the charge thus influenced.

- The present invention is particularly useful in the perforation of oil wells by the shaped charge method wherein the charges are positioned in close proximity to each' other. In the perforation of oil wells, by means of shaped charges, several methods are employed. For example, the charges may be positioned Within a re-usable steel cylinder which contains airat atmospheric pressure .serving'as a shock absorbing cushion to prevent bursting of thesteel cylinder when the charges are fired simultaneously, or the charges may be contained in individual, expendable containers connected in series to a string of explosive cord. In either case, there are times when it is desirable to a position the respective charges as close together as possible, as for example, touching each other. When shaped charges so positioned are detonated by the usual means, the addjacent jets interfere with each other because of the slight delay entailed by the sequential firing as the detonation wave proceeds along the length of the detonating cord.

The present invention provides a method of obtaining substantially simultaneous detonation of a series of closely spaced shaped charges, thereby eliminating the interference between adjacent charges.

The term substantially instantaneous detonation, as used herein, means that detonation occurs in charges in close proximity to each other at a rate faster than can be accomplished by an initiator such as Primacord or the detonation shock wave in the connecting detonating.

cord, whereas, in the present invention, the simultaneity of detonation is dependent upon the electrical energy de-,

livered to a bridge in the detonator of each charge.

This invention diifers from the method of initiation commonly used in electrical systems for detonation of. charges in proximity to one another, either series, par-: allel, or series-parallel connected, in that a condenser is charged to a high potential and is discharged through the bridges of the detonators. These bridges may be ofthe conductive explosive mixture type or fine wire type,- either of which can be initiated substantially instantane ously by a high energy surge supplied by a condenser discharge.

The phenomenon of initiation eiiected by my system, in.

contrast to the normally employed system, is that in the present system the bridge is vaporized substantially instantaneously by virtue of the passage of a high energy discharge from a condenser through the material of thebridge, whereas in previous systems the bridge materialv is heated relatively slowly as a result of its resistance to electrical energy until such time as the bridge temperature has exceeded the detonation temperature of the.

primary explosive or the initiating material which surrounds or is in contact with the bridge. The condenser can be discharged by the use of an electrical, or mechanical relay or through an electron tube (such as a thyratron) performing the same functions. The present in; vention is illustrated in, but is not limited to the embodiments shown in the accompanying drawings wherein:

FIG. 1 is a schematic view of an oil well showing the general arrangement of a firing device with respect to a shaped charge perforator and a well-servicing truck;

FIG. 2 is a wiring diagram illustrating one form ofQthe' invention wherein the condenser is at the lower end of; the conductor cable and is discharged by means of a. thyratron; "i FIG. 3 is a wiring diagram illustrating another form ofthe invention which is similar to FIG. 2 except that the condenser is discharged through a relay; FIG. 4 is a Wiring diagram illustrating still another form of the invention wherein the condenser is charged at the top of the well before being lowered into the well: and Y FIG. 5 is a wiring diagram illustrating another form of the invention which is similar to FIG. 4 except that an initiation occurring in a neighboring charge caused by initiation of the explosive in the second charge by infiuence (a term commonly used in explosive terminology) from a shock from the first charge. For example, the detonating rate for Primacord is approximately 21,000 feet per second which is approximately 3.4 microseconds per inch. The detonating rate of the explosive in the shaped charges is considerably higher and usually exceeds 25,000 feet per second, which is approximately 3.0 microseconds per inch. With the initiator of the present invention the delay between detonation of shaped charges can be measured in fractions of microseconds rather than in microseconds.

In the conventional method of detonating charges in proximity to one another the delay between initiation of the various charges is dependent upon the velocity of the condenser is discharged by a relay instead of a thyratron.

Referring to the drawings, an oil well is indicated at 1 with a casing 2 cemented at 3 above a casing shoe 4. Below the casing is open uncased hole 5 extending to the bottom 6 of the well. Within the well 1 an electric cable 7 is suspended from a tripod 8 having a sheave 9 over which the cable passes to and from a drum hoist truck 10. The lower end of the cable 7 is connected to the upper end of a cylindrical housing 11 which containsthe firing circuit, which is the subject ofthe present inYQIF tion. 3 Below the housing 11 are a number of shaped charges 12 connected in series by leads 13 and supported by the housing 11 at the lower end thereof.

FIG. 2 illustrates a charging and firing circuit in which the condenser charging device is located in the tool which goes into the well and in which a thyratron tube is used to discharge the condenser which in turn, fires the shaped charges.

A source of electrical current 13a at the top of the well is connected to the conductor cable 7 (FIG. 1) through a firing switch 14. The current available at the lower end of conductor cable 7 is relatively small, since the conductor cable is of relatively small diameter and Patented June 20,

3 has a considerable voltage drop due to its extreme length. The firing signal from the lewer end of cable 7 can be employed to discharge a condenser by the firing of a thyratron 16 which firesthe detonator bridges 17 in a series or shaped charges, not shown.

The condenser 15 can be charged by any one of several mean either at the top or the well or within the well. In FIG. 2 the latter arrangement is shown. A battery 18 furnished the power to charge the condenser 15 and to operate a shunt drive vibrator 19. In order that the firing circuit can be lowered into the well in an unarmed condition, it is desirable to provide a safety device in the circuit. In FIG. 2, this safety device is in the form of a pressure sensitive switch 20 which is normally open and is closed when subjected to a sufiicient pressure, such as the submergence pressure in the well.

A transformer 21 is used to step up the voltage from the battery 18 to the proper value for charging the condenser 15. Since a transformer will not pass direct current, a vibrator 19 is used to produce an alternating current for the transformer, illustrated in FIG. 2.

In the operation of the system illustrated in FIG. 2, if, for example, a '90 volt battery 18 is used, the condenser 15 can be charged to 1500 volts with a transformer ratio of 16.6 to 1. By closing the firing switch 14- the thyratron 16 is fired. This closes the circuit and discharges the condenser 15 through the detonator bridges 17. It should be noted that the discharge path of the condenser 15 is very short, being through the thyratron 16 and detonators 17 which are at the lower end of the cable 7. The use of a thyratron gives a substantially instantaneous closures of the discharge circuit.

3 illustrates an alternative embodiment of the in- Venti'on wherein a relay 22 is substituted for the thyratron 16 of FIG. 2. The operation of this system is similar to the operation of the system shown in FIG. 2.

FIGS. 4 and 5 illustrate still other embodiments of the invention wherein the condenser 15 is charged before being lowered into the well. In this system, it is necessary to use a condenser which can maintain its charge for several hours. The condenser can be charged by any suitable means. The discharge circuits can be either of the circuits shown in FIGS. 2 and 3. FIG. 4 illustrates the remote charging system with a thyratron type of firing, shown in FIG. 2.

FIG. 5 illustrates the remote charging system with a relay type of firing, as shown in FIG. 3.

I claim:

1. A system for perforating a well comprising the following equipment adapted 'to be lowered into the well: a plurality of shaped explosive charges, an electric deto nator means for each charge, a condenser, a firing switch and -a relay means, said condenser and detonating means and relay means being arranged in a series circuit with each other, a transformer having a primary winding and -a secondary winding, said secondary winding having an output terminal connected to said condenser, a DC. source of voltage and a vibrator coil in series with each other and with an input terminal of said primary winding, whereby voltage from said D.C. source produces alternating voltage at said secondary winding which charges said condenser; said firing switch adapted to be located outside the well; and an electric line interconnecting the relay means with said firing switch, there being a source of electric potential in said line; whereby actuation of said switch after said condenser is charged actuates said relay means and thereby discharges said condenser through said detonating means to explode the shaped charges simultaneously.

2. A system for perforating a well comprising the following equipment adapted to be lowered into the well: a plurality of shapedfexplosive charges, a detonator bridge for each charge, a condenser and a thyratron having a cathode, control grid and anode, said condenser and bridges being arranged in a series circuit with the anode and cathode of the thyrarton, a transformer having a primary winding and a secondary winding, said secondary winding having an output terminal connected to said condenser, a DC. source of voltage and a vibrator coil in series with each other and with an input terminal of said primary winding, whereby voltage from said D.C. source produces alternating voltage at said secondary winding which charges said condenser; an operating switch adapted to be located outside the well; an electric line interconnecting the said control grid with said switch; a source of electric potential connected in series with said operating switch, said electric line, and said control grid; whereby actuation of said switch after said condenser is charged fires said thyratron and thereby discharges said condenser through said bridges to explode the shaped charges simultaneously.

3. A system for perforating a well comprising the following equipment adapted to be lowered into the well: a plurality of shaped explosive charges, a detonator bridge for each charge, a condenser and a relay comprising a relay coil and contacts closable by energization of the relay coil, said condenser and bridges being arranged in a series circuit with the relay contacts, a transformer having a primary winding and a secondary winding, said secondary winding having an output terminal connected to said condenser, a DC. source of voltage and a vibrator coil in series with each other and with an input terminal of said primary winding whereby voltage from the DC. source produces alternating voltage at said secondary winding which charges said condenser; an operating switch adapted to be located outside the well; an electric line interconnecting said relay coil and said operating switch; a source of electric potential connected in series with said operating switch, said electric line, and said relay coil; whereby actuation of said switch after said condenser is charged actuates said relay coil to close the relay contacts and thereby discharge said condenser through said bridges to explode the shaped charges simultaneously.

References Cited in the file of this patent UNITED STATES PATENTS 2,331,058 Stick Oct. 5, 1943 2,370,909 Martin Mar. 6, 1945 2,703,053 Castel Mar. 1,1955

2,703,366 Tuck Mar. 1, 1955 FOREIGN PATENTS 660,285 Great Britain Nov. 7, 1951 

